`count_for_pager` is broken for id fields that aren't integers

`Table.has_id` is used to determine whether or not to use `MAX(id)` vs `COUNT(*)` in `count_for_pager`, but this only works if the `id` field is an integer.

In my schema i have an id that is a text type representing a UUID, which makes `count_for_pager` always return 0.

I think it might be safer to only use `MAX(id)` if `has_id` is true _and_ the id field is some sort of integer type
